A cross-country skier depends on a difference in static and dynamic friction on the snow to enable him to "kick and slide". When skis were made of wood, there was a reasonable ratio between static and dynamic friction on dry snow. However, when a water lubrication layer was present on the snow (damp or wet snow), the static friction was greatly reduced, making it difficult to progress by a simple "kick and slide". Ski waxes were developed to overcome this problem. By adjusting the consistency of the wax to that of the snow, it was possible to provide an enhanced grip on the snow particles while the ski was at rest, without unduly compromising the sliding friction.
With the more recent advent of plastic ski soles, with their inherent improved sliding ability, the static friction was lowered so much that waxing became essential under all snow conditions. But waxing correctly is somewhat of an art, and it is obvious that there is a need for a ski sole which will provide a satisfactory "kick and slide" function, independent of widely differing snow conditions. Accordingly there has been a serious demand for such a ski sole, and various attempts have been made to satisfy it.
The grip on the snow depends on two factors, a mechanical accommodation to the snow surface and a surface chemical adhesion. The mechanical technique has been greatly refined and consists of providing a directionally shaped surface on the ski sole in the form of backward facing steps or "fish scales" which engage the snow when the ski tends to slide backward. The deeper the steps and the more of them the better the grip but the poorer the glide.
The chemical adhesion technique has also been tried and consists of providing hydrophilic sites on the ski sole surface, (U.S. Pat. No. 3,897,074). These hydrophilic sites act through a film of water, and in that way provide climbing ability, but on dry snow some mechanical effect is also necessary.
Another method that has been tried combines both mechanical and chemical effects. The so-called mica ski sole contains many relatively large mica flakes embedded in the plastic matrix and oriented so as to provide, when abraded, a stepped surface on a micro scale. The use of mica results in the surface being hydrophilic. Such skis climb well on wet snow but glides very poorly on all but a few kinds of snow. The mica ski is disclosed in Norwegian Patent Application No. 772,044.
All of these patterned surfaces attempt to create a surface which has a low coefficient of friction in the gliding direction, with a higher coefficient in the reverse direction; hence, the idea of oriented steps, or "fish scales" or mica structures. However, all of these surfaces suffer from the same compromise between climbing and gliding properties.
A no wax ski will not be satisfactory unless it can perform on most snow conditions as well as a well-waxed ski, something that until now has been considered virtually impossible.